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_lwp_cond_wait(2)                System Calls                _lwp_cond_wait(2)



NAME
       _lwp_cond_wait, _lwp_cond_timedwait, _lwp_cond_reltimedwait - wait on a
       condition variable

SYNOPSIS
       #include <sys/lwp.h>

       int _lwp_cond_wait(lwp_cond_t *cvp, lwp_mutex_t *mp);

       int _lwp_cond_timedwait(lwp_cond_t *cvp, lwp_mutex_t  *mp,  timestruc_t
       *abstime);

       int    _lwp_cond_reltimedwait(lwp_cond_t    *cvp,    lwp_mutex_t   *mp,
       timestruc_t *reltime);

DESCRIPTION
       These functions are used to wait for the occurrence of a condition rep-
       resented  by an LWP condition variable. LWP condition variables must be
       initialized to 0 before use.

       The _lwp_cond_wait() function atomically releases the LWP mutex pointed
       to by mp and causes the calling LWP to block on the LWP condition vari-
       able  pointed  to  by  cvp.  The  blocked  LWP  may  be   awakened   by
       _lwp_cond_signal(2),  _lwp_cond_broadcast(2),  or  when  interrupted by
       delivery of a signal. Any change in value  of  a  condition  associated
       with  the  condition  variable  cannot  be  inferred  by  the return of
       _lwp_cond_wait() and any such condition must be re-evaluated.

       The _lwp_cond_timedwait()  function  is  similar  to  _lwp_cond_wait(),
       except  that the calling LWP will not block past the time of day speci-
       fied by abstime. If the time  of  day  becomes  greater  than  abstime,
       _lwp_cond_timedwait() returns with the error code ETIME.

       The  _lwp_cond_reltimedwait()  function is similar to _lwp_cond_wait(),
       except that the calling LWP will not block past the relative time spec-
       ified  by reltime. If the time of day becomes greater than the starting
       time of day plus reltime,  _lwp_cond_reltimedwait()  returns  with  the
       error code ETIME.

       The  _lwp_cond_wait(),  _lwp_cond_timedwait(),  and _lwp_cond_reltimed-
       wait() functions always return with the mutex locked and owned  by  the
       calling lightweight process.

RETURN VALUES
       Upon  successful  completion, 0 is returned. A non-zero value indicates
       an error.

ERRORS
       If any of the  following  conditions  are  detected,  _lwp_cond_wait(),
       _lwp_cond_timedwait(), and _lwp_cond_reltimedwait() fail and return the
       corresponding value:

       EINVAL          The cvp argument points to  an  invalid  LWP  condition
                       variable  or  the  mp argument points to an invalid LWP
                       mutex.



       EFAULT          The mp, cvp, or abstime argument points to  an  illegal
                       address.



       If   any   of   the   following   conditions  occur,  _lwp_cond_wait(),
       _lwp_cond_timedwait(), and _lwp_cond_reltimedwait() fail and return the
       corresponding value:

       EINTR           The call was interrupted by a signal or fork(2).



       If  any  of  the  following conditions occur, _lwp_cond_timedwait() and
       _lwp_cond_reltimedwait() fail and return the corresponding value:

       ETIME           The time specified inabstime or reltime has passed.



EXAMPLES
       Example 1: Use the _lwp_cond_wait() function in  a  loop  testing  some
       condition.

       The  _lwp_cond_wait()  function is normally used in a loop testing some
       condition, as follows:

       lwp_mutex_t m;
       lwp_cond_t cv;
       int cond;
       (void) _lwp_mutex_lock(&m);
       while (cond == FALSE) {
               (void) _lwp_cond_wait(&cv, &m);
       }
       (void) _lwp_mutex_unlock(&m);


       Example 2: Use the _lwp_cond_timedwait() function  in  a  loop  testing
       some condition.

       The  _lwp_cond_timedwait()  function  is  also  normally used in a loop
       testing some condition. It uses an absolute timeout value as follows:

       timestruc_t to;
       lwp_mutex_t m;
       lwp_cond_t cv;
       int cond, err;
       (void) _lwp_mutex_lock(&m);
       to.tv_sec = time(NULL) + TIMEOUT;
       to.tv_nsec = 0;
       while (cond == FALSE) {
               err = _lwp_cond_timedwait(&cv, &m, &to);
               if (err == ETIME) {
                       /* timeout, do something */
                       break;
               SENDwhom}
       }
       (void) _lwp_mutex_unlock(&m);


       This example sets a bound on  the  total  wait  time  even  though  the
       _lwp_cond_timedwait()  may  return  several  times due to the condition
       being signalled or the wait being interrupted.

       Example 3: Use the _lwp_cond_reltimedwait() function in a loop  testing
       some condition.

       The  _lwp_cond_reltimedwait()  function is also normally used in a loop
       testing some condition. It uses a relative timeout value as follows:

       timestruc_t to;
       lwp_mutex_t m;
       lwp_cond_t cv;
       int cond, err;
       (void) _lwp_mutex_lock(&m);
       while (cond == FALSE) {
               to.tv_sec = TIMEOUT;
               to.tv_nsec = 0;
               err = _lwp_cond_reltimedwait(&cv, &m, &to);
               if (err == ETIME) {
                       /* timeout, do something */
                       break;
               }
       }
       (void) _lwp_mutex_unlock(&m);


SEE ALSO
       _lwp_cond_broadcast(2),       _lwp_cond_signal(2),        _lwp_kill(2),
       _lwp_mutex_lock(2), fork(2), kill(2)




SunOS 5.10                        13 Apr 2001                _lwp_cond_wait(2)